Friction Modifier
Reducing the friction between two surfaces of plastic film or between the film and manufacturing equipment allows for efficient winding and converting. Slip additives are incorporated into polymer resins to provide this lubrication without compromising the base properties of the substrate. These agents provide the lubrication required to move webs smoothly over rollers and prevent sticking during the bag making process.
Surface Development
Most common varieties are fatty acid amides that are blended into the melt during the extrusion process. As the film cools and ages, these molecules migrate from the bulk of the polymer to the surface where they form a microscopic layer of lubricant. This blooming process is time-dependent and temperature-dependent, meaning the final friction level is not achieved until several hours or days after the film is produced.
The rate of migration depends on the molecular weight of the additive and the crystallinity of the base resin, with higher density materials slowing the movement of the slip molecules.
Application Constraint
High concentrations of these chemicals can interfere with the wetting of the surface by inks or adhesives during printing and lamination. If the slip level is too high, the film may also become difficult to track through the machine, leading to registration errors or winding defects. Testing often involves measuring both the static and kinetic coefficient of friction to ensure the material meets the requirements of the specific converting line.
